1. Field of the Disclosure
The disclosure relates to a method for tightness testing wherein a test object filled with test gas is inserted into a test chamber and wherein, by use of a test gas sensor, a gas mixture made of a test gas withdrawn from the test chamber and of a carrier gas, is examined for the presence of test gas.
2. Discussion of the Background Art
The disclosure further relates to a method for tightness testing wherein an evacuated test object is exposed to the external influence of a test gas, and wherein, by use of a test gas sensor, a gas mixture made of a test gas withdrawn from the test object and of a carrier gas, is examined for the presence of test gas.
A known method for integral tightness testing provides that the test object filled with test gas is to be placed into a test chamber. The test chamber will be evacuated by a vacuum system, with a test gas sensor being integrated in said vacuum system. A typical test gas is helium, which presently is detected with the aid of a mass spectrometer. Testing for helium will require high vacuum conditions wherein the pressure p has to be less than 10−4 mbar.
A further method for integral tightness testing provides that the test object will be evacuated and be exposed to the external influence of a test gas. Using a vacuum system connected to the test object, it will be possible to perform a mass spectroscopic detection of the test gas.
Tightness testing systems have a time constant which normally is dictated by the application. The time constant indicates the time period until stable signal conditions are reached. It is determined by the volume of the test chamber and by the test gas suction capacity at the test chamber:τ=V/S     τ: System time constant (63%-time)    V: Volume of the test chamber    S: Suction capacity of the pump for the test gas
The smallest leak rate measurable by a system is dependent on the smallest test-gas partial pressure that the system is able to detect. The test gas pressure prevailing in the respective application is determined as follows:p=Q/S     p: Partial pressure of the test gas    Q: Leakage rate of the test gas from the test object    S: Suction capacity of the pump for the test gas
Herein, an antagonism exists: it is not possible to increase the test-gas partial pressure and simultaneously reduce the time constant. A large test-gas suction capacity, although indeed effective to reduce the signal reaction time, will also reduce the test gas pressure and thus the sensitivity of the system.
Described in WO 2005/054806 A1 (Sensistor) is a vacuum test system according to the preamble of the respective claims wherein a test gas is to be introduced into a test chamber or into the test object. Into the respective other one of said two cavities, a carrier gas is inserted. If a leak should happen to exist on the test object, test gas will enter the carrier gas flow and be conveyed together therewith to a compressor pump. Connected to the outlet of the pump is a test gas sensor operating under atmospheric pressure. Applying the carrier gas method, the test-gas partial pressure of the compressed gas mixture is measured downstream of the pump. Thereby, a high system sensitivity can be achieved because the test-gas partial pressure of the compressed gas behind the pump is high. By the compressing pump, the total pressure existing in the test chamber and respectively in the interior of the test object will be increased to 1000 mbar at the pump outlet.
It is an object of the disclosure to provide a method for tightness testing wherein the quantity of the required test gas is reduced.